A process gas compressor has a housing and a rotor which is accommodated in the housing. The rotor has a shaft which is mounted at the longitudinal ends thereof outside the housing. As a result, the shaft passes at the longitudinal ends thereof through the housing, wherein the shaft is sealed there from the housing by a shaft seal. The inside of the process gas compressor is therefore separated from the atmosphere. The construction of the shaft seal is conventionally such that a gas separation is arranged first, followed by an oil separation, as viewed from the inside of the process gas compressor. The inside of the process gas compressor, the process side, is separated from the atmosphere by means of the shaft seal and from the bearing region by means of the oil separation. The shaft seal is constructed, for example, as a gas-lubricated rotating mechanical seal which is designed as a tandem seal.
A tandem seal is constructed from two gas-lubricated rotating mechanical seals which each have a sliding ring, which is fastened to the housing, and a counter ring, which is fastened to the shaft. Each sliding ring is arranged axially directly adjacent to the associated counter ring thereof, forming an axial gap. The rings are arranged in the tandem seal in such a manner that the process side is sealed from a flare pressure by the primary seal. The separation from the atmosphere is brought about with the secondary seal, wherein the secondary seal is additionally provided as redundancy to the primary seal in the event of failure of the primary seal. Seal gas which is used for sealing the axial gaps is introduced between the two counter rings. In order to separate the bearing region, a tertiary seal, for example, which can be constructed, for example, as a labyrinth seal or a carbon ring seal, is provided as the oil separation. The tertiary seal is acted upon with a seal gas, as a result of which the sealing of said tertiary seal is brought about.
Process gas can be used as the seal gas for the primary seal, and air or nitrogen can be used for the secondary seal. During the operation of the process gas compressor, leakage gas occurs because of a leakage of the primary seal and the secondary seal. The leakage gas is a gas mixture consisting of the process gas and the seal gas together with air, wherein the leakage gas is conventionally conducted away to the atmosphere or to a flare. These two variants are problematic for the environment by being associated with undesirable emissions to the surroundings. Although the provision of a system for separating the process gas from the leakage gas and for recycling the process gas into the process provides a remedy, such a system is, however, energy-intensive and is associated with high costs.